Coaxial cathode-anode electron tube with channel-shaped control grids for the beaming structure



Aug. 1, 1967 D. DOOLITTLE ETAL 3,334,257 COAXIAL CATHODE-ANODE ELECTRONTUBE WITH CHANNEL-SHAPED CONTROL GRIDS FOR THE BEAMING STRUCTURE FiledJan. 4, 1966 Howard D. Dooliiiie Helmui' Longer,

INVENTORS' 7 United States Patent 3,334,257 COAXlAL CATHODE-ANODEELECTRON TUBE WITH CHANNEL-SHAPED CONTROL GRIDS FOR THE BEAMINGSTRUCTURE Howard D. Doolittle and Helmut Langer, Stamford, Conn.,assignors to the United States of America as represented by theSecretary of the Army Filed Jan. 4, 1966, Ser. No. 518,748 3 Claims.(Cl. 313-69) This invention relates to improvements in beam focusingelectron tubes and has particular reference to pulse beamed tubes havinga novel electrode structure.

The present invention is directed to means for modifying the electricfield in the cathode anode space in order to increase the electron flowfrom the cathode, without an increase in the positive potentials appliedto the control grid and anode during the concluding cycle; still at highcurrent flow from the cathode, the part which will result in current tothe control-grid is still kept at a minimum so that the emittingelectron beaming structure will supply high cathode current densitieswith lower tube drive requirements.

It has previously been proposed in US. Patent No. 2,932,754, issued toJ. H. O. Harries et al., Apr. 12, 1960, to modify the shape of theelectric field in the cathodeanode space whereby the electrontrajectories which were previously turned back toward the control gridare instead caused to be directed toward the anode. This is accomplishedby providing the screen grid wires with radially extending fin-likecross-sectional shapes which not only direct the electrons from thecathode to the anode in the desired manner but also maintain a highvalue of mu and reduce the screen grid to anode capacity. This inventionfurther enhances the quantity of electrons available at the anode byplacing novel channel shaped control grid electrodes along with thepreviously disclosed fin shaped screening grid in the cathode-anodespace whereby a stronger and more uniform field is introduced in frontof the cathode slot and has a more pronounced beaming effect on theelectron stream from the cathode.

It is, therefore, an object of this invention to provide an electrontube with a predetermined shaped control grid which introduces astronger and more uniform field in front of the cathode slot.

Another object of this invention is to provide a modification ofespecially the cathode-grid field of an electron tube to give a morepronounced beaming effect on the electron stream from the cathode.

Another object of this invention is to provide a more eflicient beamedtriode having an amplification factor which is substantially doubledthus requiring less negative cut-off voltage during the non-conductivecycle.

A further object is to provide a more efficient beamed triode whichrequires lower total drive power requirements during the conductingcycle.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings, wherein:

FIGURE 1 is a horizontal sectional view of a typical beamed triode withmodifications according to the present invention.

3,334,257 Patented Aug. 1 1 967 The electrode structures embodying thepresent invention include a cathode structure 5, a control gridstructure 7, a screen grid structure 9 and an anode structure 11, all ofwhich are coaxial structures mounted one within another as shown andsuitably supported so as to maintain their respective predeterminedspace relations.

The cathode structure embodies a hollow cylindrical cathode 13 withinwhich is located a heating coil or filament 15. The filament 15 issuitably connected to a source of electrical energy whereby it willradiantly heat the cathode 13 for liberation of electrons, as will bedescribed.

' The outer surface of the cathode 13 is provided with a FIGURE 2 is anenlarged fragmentary horizontal secv plurality of longitudinal grooves17 which are spaced substantially equidistant apart throughout thecircumference of the cathode. The side walls 19 of the grooves 17 extendsubstantially radially with respect to the longitudinal axis of thecathode, and the bottoms of the grooves 17 are preferably slightlyconcave, being curved in a trans verse direction as shown in FIGURE 2.Deposited upon the bottom of each groove 17 is a layer 21 of a selectedelectron emissive material such as one of the oxides com-- monly usedfor this purpose in the electron tube industry. When the cathode isheated and a relatively high suitable potential applied in the normalmanner across the tube, electrons are emitted by the material 21 and arecaused to flow in a direction toward the anode.

Opposite each land 23 between the respective grooves 17 is located arespective channel shaped member 25 of the control grid 7. The channels25 extend parallel to the cathode and to each other and in predeterminedspaced relation thereto, and are generally U-shaped in crosssectionhaving a width consistant with the widths of the lands 23 such that thechannels 25 are as close to the sides of the electron beams emanatingfrom the emissive material 21 in grooves 17 as is compatible withnon-interception of the beams by the control grid.

' Radially spaced outwardly of each of the control grid channels 25 is arespective screen grid member or wire 27, the wires 27 being located inpredetermined spaced relations to both the anode 11 and control gridchannels 25.

The anode 11 is a hollow cylindrical body of copper which encloses thegrids and cathode and forms in itself a large portion of the tubeenvelope.

The several electrodes are all supplied with various potentials byconductive means clearly shown and described in the above mentioned US.Patent to Harries et al. The tube is adapted to be operated byimpressing the desired potential between the anode and cathode, applyinga relatively high positive potential to the control grid, and applyingto the screen grid a zero potential with respect to the cathode.Therefore, electrons emitted by the material 21 in the cathode grooves17 will be focused, under the influence of the side walls 19 of thegrooves, toward the anode 11. The control grid channels 25, located justout of the direct trajectories of the electrons, will not normallyintercept the electrons. The curvature of the emitting surface also aidsin properly focusing the electron beam because of the fact thatelectrons leave an emitting surface substantially normal to the surfaceat the point of emission.

In this type of tube structure, the positive control grid normally willnot intercept any primary electrons until they have travelled past thisgrid and have reversed their directions and been trapped, therefore thefin-like shaped screen grid 9 is used and spaced between in thecathodeanode spacing as proposed previously by the above mentionedpatent to Harries et al. to prevent the reversal of many of the electrontrajectories.

It has been found that the control grid can be modified to have agenerally U-shaped cross section which in turn provides modification ofespecially the cathode-grid field.

This modification introduces a stronger and more uniform field in frontof the cathode slot and has a more pronounced beaming effect on theelectron stream from the cathode. Using the channel shaped control gridelectrode, the maximum positive potential, which will accelerate theelectron beam from the cathode is by at least 12% higher at a givendrive potential than using the conventional round electrode. Theelectron delay potential in the screen grid-anode region is by at least5% lower using a channel shaped electrode grid than when using a roundcontrol grid electrode. The amplification factor mu of this structure issubstantially doubled, which requires less negative cut-off voltageduring the non-conductive cycle and lowers the total drive powerrequirements during the conducting cycle.

The dimensions and spacing of the particular elements are substantiallythe same as that disclosed in Harries et al. with the exception of thecontrol grid channels which are approximately .070" to .100 wide and.060" deep radially.

While the invention has been described with reference to a preferredembodiment thereof, it will be apparent that various modifications andother embodiments thereof will occur to those skilled in the art inlight of the present disclosure. Accordingly, it is desired that thescope of this invention be limited only by the appended claims.

What is claimed is:

1. In an electron tube, electrode beaming structures comprising a hollowanode, a cylindrical cathode coaxial within the anode, said cathodehaving on its outer surface a plurality of alternately located electronemitting and non-emitting areas having lands therebetween and means forfocusing electrons from the emitting areas into beams directed towardthe anode, said cathode and anode being operable at different knownpotentials, a screen grid means located in predetermined spaced relationbetween said anode and said cathode, and a control grid means located inpredetermined spaced relation between said screen grid means and saidcathode, said control grid means comprised of channel shaped membersdisposed adjacent to the non-emitting areas of said cathode and beingoperated at relatively high positive potentials.

2. In an electron tube as set forth in claim 1, said screen grid meanscomprised of members radially aligned with said control grid channels,said members being adapted to be maintained during operation of saidtube at substantially cathode potential, said members being ribbonlikein shape to form electric fields therearound which aid electron flow tosaid anode and prevents substantial trapping of electrons between grids.

3. In an electron tube as set forth in claim 2 wherein said lands are nowider than said channel shaped members of said control grid means.

No references cited.

JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

1. IN AN ELECTRON TUBE, ELECTRODE BEAMING STRUCTURES COMPRISING A HOLLOWANODE, A CYLINDRICAL CATHODE COAXIAL WITHIN THE ANODE, SAID CATHODEHAVING ON ITS OUTER SURFACE A PLURALITY OF ALTERNATELY LOCATED ELECTRONEMITTING AND NON-EMITTING AREAS HAVING LANDS THEREBETWEEN AND MEANS FORFOCUSING ELECTRONS FROM THE EMITTING AREAS INTO BEAMS DIRECTED TOWARDTHE ANODE, SAID CATHODE AND ANODE BEING OPERABLE AT DIFFERENT KNOWNPOTENTIALS, A SCREEN GRID MEANS LOCATED IN PREDETERMINED SPACED RELATIONBETWEEN SAID ANODE AND SAID CATHODE, AND A CONTROL GRID MEANS LOCATED INPREDETERMINED SPACED RELATION BETWEEN SAID SCREEN GRID MEANS AND SAIDCATHODE, SAID CONTROL GRID MEANS COMPRISED OF CHANNEL SHAPED MEMBERSDISPOSED ADJACENT TO THE NON-EMITTING AREAS OF SAID CATHODE AND BEINGOPERATED AT RELATIVELY HIGH POSITIVE POTENTIALS.